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Re: software or hardware RAID?

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Hi All

Just would like to know conclusion here ,

What is best RAID method (Software Or Hardware) for Postgres DB and what level ?

Thanks,
Raj




On Sat, Mar 23, 2019 at 3:12 PM Kenneth Marshall <ktm@xxxxxxxx> wrote:
On Sat, Mar 23, 2019 at 12:09:11PM +0000, Rory Campbell-Lange wrote:
> On 17/03/19, Rory Campbell-Lange (rory@xxxxxxxxxxxxxxxxxx) wrote:
> > We aren't sure whether to use software MDRaid or a MegaRAID card.
> >
> > We're buying some new Postgres servers with
> >
> >     2 x 240GB Intel SSD S4610 (RAID1 : system)
> >     4 x 960GB Intel SSD S4610 (RAID10 : db)
> >
> > We'll be using Postgres 11 on Debian.
> >
> > The MegaRAID 9271-8i with flash cache protection is available from our
> > provider. I think they may also have the 9361-8i which is 12Gb/s.
> >
> > Our current servers which use the LSI 9261 with SSDs and we don't see
> > any IO significant load as we are in RAM most of the time and the RAID
> > card seems to flatten out any IO spikes.
> >
> > We use MDRaid elsewhere but we've never used it for our databases
> > before.
>
> Apologies for re-heating this email from last week. I could really do with the
> advice.
>
> Has anyone got any general comments on whether software RAID or an LSI card
> is preferable?
>
> We will be replicating load on an existing server, which has an LSI 9261 card.
> Below is some stats from sar showing a "heavy" period of load on vdisk sda
>
>       00:00:01  DEV     tps  rd_sec/s  wr_sec/s  avgrq-sz  avgqu-sz     await     svctm     %util
>       14:15:01  sda  112.82    643.09  14986.24    138.53      2.09     18.50      0.25      2.86
>       14:25:01  sda  108.52    270.17  15682.94    147.01      1.87     17.22      0.25      2.73
>       14:35:01  sda  107.96    178.25  14868.52    139.37      1.70     15.73      0.23      2.53
>       14:45:01  sda  150.97    748.94  16919.69    117.03      1.83     12.11      0.22      3.28
>
> Thanks for any advice.
> Rory

Hi Rory,

The main reason, in my opinion, to use a HW RAID card is for the NVRAM
battery backed cache to support writing to traditional spinning disks.
Since your SSDs have power-loss support, you do not need that and the HW
RAID controller. For database use, you would almost certainly be using
RAID 10 and software RAID 10 is extremely performant. I am in the middle
of setting up a new system with NVMe SSD drives and HW RAID would be a
terrible bottle-neck and software RAID is really the only realistice
option.

Regards,
Ken


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